Many communication networks, such as networks designed according to the Ethernet and IEEE 802.11b standards, transmit data in packets. These networks use many different methods to access the physical medium. For example, one typical access method uses a carrier sense, multiple access/collision avoidance (CSMA/CA) protocol. Because these methods transmit packets at random times, and because of transmission delays, one problem that arises is detection of and synchronization to the packets in a receiver. Synchronization is necessary to properly process the blocks of data in each packet. Thus, most transmitters send a preamble, which is a particular sequence of symbols, to enable packet detection and synchronization in the receiver. Furthermore, the receiver can use the preamble to estimate several related parameters, such as a frequency offset and channel state information.
Detecting and synchronizing to the packets and estimating the related parameters becomes more difficult, however, when the symbols are transmitted over different frequency sub-bands according to a frequency hopping pattern. In such systems, each network uses a different sequence of sub-bands to transmit and receive packets, called a “frequency hopping pattern,” to reduce collisions between devices belonging to different networks. A transceiver using this mode of transmission over several frequency bands is called “frequency hopping” or “time frequency interleaving.” A new device attempting to join a network, however, does not know a priori the sequence being used by the network.
What is needed, therefore, are techniques for devices joining a frequency hopping network for detecting and synchronizing to frequency hopped packets.